L’action inductrice du chordo-mésoblaste au cours de la gastrulation et de la neurulation et les effets de la culturein vitrosur ses manifestations

Abstract

ABSTRACTOne species of Urodele, Trituras alpestris, was used. The inducing capacities of the anterior chordal zone of the archenteron roof were studied in vitro by the ectoblastic ‘sandwich ‘method. The inducing material was taken from different stages of gastrulae and neurulae. The duration of induction (16–24 hours) had been determined by the results of the author’s previous experiments: it was sufficient to provoke a clear reaction in the ectoblast, but too short for the chordomesoblast to exert fully its specific regional inductive capacity.When the period of induction was at an end, the two layers of the ‘sandwich ‘were separated to remove the inductor, and the layers were allowed to develop separately in Holtfreter’s solution. No difference was found in the inductive capacities of the dorsal and ventral surfaces of the archenteron roof.Histological examination of the neural structures produced by the expiants confirmed the results obtained previously in analogous experiments involving transplants to the embryo. The inductive power of the chordomesoblast becomes considerably modified during gastrulation and neurulation. Its feeble power of inducing a forebrain is a more or less delayed acquisition, which only comes into action at the time when the process of neural induction is almost achieved in the embryo. It always possesses, however, a predominant power of inducing deutencephalon and spinal cord. The induction by the chordomesoblast of cerebro-sensory complexes which are exclusively acrencephalic becomes possible only when one dissociates the effects of the two activities manifested by the inductor.A comparison of these results with those of the author’s previous experiments shows that it is easier for the chordomesoblast to induce a forebrain in ectoblast cultivated in vitro than in grafts implanted on the archenteron roof and then transplanted to the ventral surface of another embryo. In the first case, not only are acrencephalic formations much more frequent, but one can obtain them with a younger chordomesoblast. The saline solution of Holtfreter has a feeble acrencephalogenic action on the neural structures which have resulted from an insufficient induction and which are still labile in the direction of their development.The author reviews the conception of neural induction held by Nieuwkoop, and the similar interpretation adopted by Johnen to explain the results of her experiments.